Scientific Journal of Frontier Chemical Development June 2013, Volume 3, Issue 2, PP.25-29
Copper-Catalyzed Allylic Oxidation of Cyclohexene with Molecular Oxygen Xu Zhang 1, Rong Yi 1, Tian Chen 1, Shichun Ni 2, Genlin Wang 2, Lei Yu #, 1, 2 1. School of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou, 225002,People’s Republic of China 2. Jiangsu Yangnong Chemical Group Co. Ltd., Yangzhou, 225009, People’s Republic of China #Email: yulei@yzu.edu.cn
Abstract Copper-catalyzed aerobic allylic oxidation of cyclohexene under solvent-free conditions leads to 2-cyclohexenol and 2cyclohexenone, the important intermediates in chemurgy. This pathway is suitable for industrial production, owing to the high conversion rate and selectivity, the solvent-free conditions, the cheap catalyst and the environment-friendly oxidant and procedure. Keywords: Catalysis; Copper; Allylic Oxidation; Aerobic Oxidation; Cyclohexene.
1 INTRODUCTION The allylic oxidation of olefins is one of the most important topics in both academic and industrial researches. In this process, olefins are converted to unsaturated alcohols or ketones while the C=C bond is preserved.1 The allylic oxidation of cyclohexene is a typical example, since the products 2-cyclohexenol and 2-cyclohexenone are very useful compounds in chemurgy.2 Up to the present, the catalytic allylic oxidation of cyclohexene has drawn much attention and many effective catalysts have been developed, such as metal nanoparticles,3-5(Table 1, entries 1-3) metal–organic frameworks,6(Table 1, entry 4) metal porphyrin complexes 7-9(Table 1, entries 5-7) and non-metal catalysts.10(Table 1, entry 8) However, some of the above catalysts have resulted in low conversion rates and low selectivity, 6 on the other hand, many of them require organic solvents 3-5, 7-10, 12 and chemical oxidants.3 Recently, gold has also been found to have strong catalic ability in the allylic oxidation of cyclohexene. 11-13(Table 1, entries 911) However, the high price hinders their large scale applications. The ideal catalytic oxidation process suitable for industrial production expected to employ molecular oxygen as the oxidant, simple and abundant catalyst, is carried out in solvent-free conditions.14 Our group has been trying to achieve this goal in cyclohexene’s oxidation for a long time. Recently, the transition metal-catalyzed allylic oxidation of cyclohexene has been investigated by molecular oxygen and it was found that catalyzed by copper, the oxidation of cyclohexene by molecular oxygen led to 2cyclohexenol and 2-cyclohexenone with high conversion rate and selectivity in solvent-free conditions.(Table 1, entry 12) Herein, our findings were available. TABLE 1 THE ALLYLIC OXIDATION OF CYCLOHEXENE REPORTED BY RECENT LITERATURES.
OH [O] cat. 1 Entry 1 2 3 4 5 6 7
Catalyst CuO CoO CoHAP-γ-Fe2O3 Cu/Co-MOFs Fe-Por Mn-Por Ru-Por
O +
2 Oxidant TBHP O2 H2O2 O2 O2 O2 O2
Solvent CH3CN c-C6H12 MeCN MeOH/MeCN MeCN MeCN - 25 www.sjfcd.org
3 Conv. (%) 99 97 88 33 100 72 100
2+ 3 Select. (%) 95 80 81 44 99 67 94
Ref. 3 4 5 6 7 8 9